Acids are used to catalyze reactions in a number of different syntheses in the refining, chemical, petrochemical and pharmaceutical industries among others. Acids may also be formed as a result of syntheses, as reaction byproducts. Following the synthesis, it is often desired to eliminate the acid from the fluid. Elimination of the acid from the fluid is traditionally accomplished by means of base neutralization which typically involves a two-step process, one of neutralization and another of excess neutralizer and neutralization byproduct removal. That is, a base in the form of a liquid or a solid is added to the fluid to neutralize the acids. Typically an excess of the base neutralizer must be added to assure complete removal of acid. As a result of the neutralization of the acid by the base neutralizer, salt byproducts are formed. Following the acid neutralization process, the excess base neutralizer and salt byproducts must be removed.
If the base is a solid, the excess base and salts are typically removed by filtration. If the base is a liquid and a separate phase from the fluid, the neutralization is generally accomplished in columns where the base is dispersed into the product stream to facilitate the neutralization. The excess base and reaction byproducts are subsequently removed by means of a two-phase separator. Since an excess of the neutralizing compound must be added, the specific gravity between the two phases becomes very close and difficult to separate via conventional two-phase separators. Therefore, these devices are not very efficient at accomplishing a complete separation of the two phases. As a result, there is typically some base carryover from the two-phase separator, which results in the need for a water-wash tower designed to further separate the two phases.
A disadvantage of the above conventional two-stage acid neutralization process is that each of the steps has associated capital costs for the hardware such as towers and reaction tanks, and operating costs. A further disadvantage is the cycle time associated with the steps of neutralization and removal of excess neutralizer and neutralization byproducts. A further disadvantage is the necessity of adding a considerable excess of neutralizing or extracting agent, resulting in a two phase system that is very close in specific gravity between the two phases and therefore very difficult to separate using conventional two-phase separators such as coalescers, mesh-pads or vane packs, residence time devices, centrifuges etc. As a result of the shortcomings of the above conventional acid catalyst removal techniques, there is a need for a process for selective removal of the unwanted materials such as acids that overcomes these disadvantages.
The present invention provides a process for the removal of an unwanted liquid from a fluid and particularly an acid from the fluid by introducing a relatively small volume of polar liquid to extract the acid from the primary phase fluid through a hydrophilic interaction between the polar liquid and the acid. The extractive fluid may have a specific gravity very close to that of the primary phase fluid. Specifically, this invention relates to the process of creating a dispersion of an extractive liquid that is substantially immiscible in the fluid to hydrophilicly interact with the acid in the fluid, to form an acid-rich liquid phase that is stably dispersed in the primary phase fluid. This stable dispersion, may be defined as a stable suspension of a discontinuous liquid phase within another continuous liquid phase, wherein the discontinuous liquid phase comprises droplets which remains dispersed or suspended in the continuous liquid phase for an extended period, the droplets not separable by conventional liquid/liquid separation technologies—such as filter-coalescers, residence time coalescers with mesh-pads or vane-packs, centrifuges etc. This stable dispersion functions to facilitate the intimate mass-transfer between the primary and secondary phases.
As an example, the above-mentioned process can be used with a dispersion comprising droplets of a discontinuous liquid phase having diameters in the 0.1-3 micron range, or smaller although larger droplets having a diameter extending up to 10 micron range are also possible, as long as the droplets remain dispersed or suspended. Following the dispersion, the present invention uses a coalescer such as a porous medium to capture, coalesce, and separate the acid-rich liquid in the form of droplets from the fluid.
Although other embodiments of a porous medium may be used to capture the droplets, in the present invention the porous medium is preferably constituted with fibers of sufficient dimensions to capture these droplets. The aforementioned fibers are typically on the order of magnitude of the droplets, that is, the porous medium usually contains of fibers that have diameter in the 0.5-2 microns range although it is conceivable that fibers of other dimensions can also be used.
One of the advantages of the present invention is that once the water-acid droplets have been removed into a continuous secondary phase, this secondary phase can be dehydrated to remove some of the water so that the acid can be reused for future applications thus eliminating waste.